1. Field of the Invention
The present invention relates to a magnetic disk drive unit and a production method therefor which is superior in shock resistance, light weight and portability.
2. Description of the Related Art
The conventional magnetic disk drive unit has a construction for enclosing a magnetic disk and a magnetic head for reading and writing information on the magnetic disk, within a metallic body generally called as a base and a cover. Such magnetic disk drive unit may have a construction as illustrated and disclosed in Japanese Unexamined Patent Publication No. Heisei 3-207076. The construction will be shown in FIG. 7.
In FIG. 7, a motor 26 with a magnetic disk 24 is secured within a base 38 made of aluminum by means of screws. Then, a carriage 30 mounting a magnetic head 28 is fixed on the base 38 together with a magnetic circuit 166 by screws. In addition, a flexible circuit board 90 is fixed on the base 38 by screws. Finally, a cover 32 is fitted over and fixed by screws. The construction set forth above is a portion referred to as DE (disk enclosure). The DE is completely sealed except for ventilation aperture with a filter in order to prevent penetration of the foreign matter.
As the magnetic disk drive unit, a PCBA (circuit package) 88 is externally fitted on the DE and is connected to the flexible circuit board 90 for inputting and outputting a signal from the magnetic head.
In such magnetic disk drive unit, the base, the cover as well as the carriage and motor are required high precision and rigidity. Therefore, these components are formed of a metal, such as s aluminum, stainless or the like and are designed to provide a thickness as thick as possible.
As a result, in case of the magnetic disk drive unit employing a 3.5 inch disk, a weight becomes 500 g to 1000 g as a whole. The drive is substantially heavy to handle as precise instrument.
On the other hand, upon handling, if falling down of the magnetic disk drive unit is accidentally caused, since the magnetic disk drive unit is covered by metal, an impact is directly transmitted to the major component (carriage, motor and so forth) housed therein.
Here, reason why high precision and rigidity is required and reason why the PCBA is mounted outside of the DE will be discussed briefly.
Concerning the dimensional precision, the magnetic disk drive unit achieves high recording density by floating the magnetic head on the magnetic disk in low floating amount in order of several tens nm. In order to stably maintain low floating amount, a relative height between an arm, on which the magnetic disk is mounted, and the disk surface has to be set strictly. If significant error is caused in the relative height, the magnetic head may be tilted in floating condition, and load to bias the magnetic head toward the magnetic disk may be varied to cause difficulty in maintaining low floating amount. On the other hand, by long period use, damage, such as head crush can be caused.
Therefore, it is generally required to manage an error of relative height between the arm and the disk to be less than or equal to 30 xcexcm to 50 xcexcm. In order to realize such tolerance, it is not only required to increase dimensional precision of the carriage and motor but also required high precision for the base mounting the arm and disk. The base is formed of aluminum. Upon manufacturing, the base is formed by aluminum die casting. In case of casting surface of aluminum die casting, it is difficult to achieve surface precision less than or equal to 50 xcexcm. Therefore, a surface to be a reference for mounting the carriage or motor, re-working is effected to achieve the foregoing precision.
On the other hand, in the magnetic disk drive unit nowadays, a ramp load system, in which the magnetic disk is retracted in a ramp provided outside of the magnetic disk upon stand-by state of the magnetic head, is employed. In this case, it is also required to strictly set the relative height between the ramp and the magnetic disk. The ramp is set above 100 xcexcm to 200 xcexcm. Upon loading the magnetic head, the magnetic head is slid on the magnetic disk, and upon unloading the magnetic head, the magnetic head is retracted to the retracted position. Therefore, if the relative height is contains an error, the magnetic head may contact on the disk surface of the magnetic disk upon loading or the magnetic head and the tip end of the ramp may contact to make it impossible to return to the retracted position.
Therefore, it is required to precisely set the height of a base surface on the base to mount the ramp by reworking.
The foregoing relative height relationship may be greater according to increase number of disks for accumulation of tolerance. Furthermore, inclination may also be accumulated to cause difficulty in management for achieving necessary precision.
In the conventional magnetic disk drive unit, the dimensional precision has to be strictly managed by reworking the metallic base.
Next, discussion will be given for demand for high rigidity in the magnetic disk drive unit.
In the recent magnetic disk drive disk unit, recording density is increasing to be higher and higher and a track pitch has reached in the extent of 1 xcexcm. In order to realize such high recording density, development has been progressed to make fluctuation 3"sgr" in positioning precision of the magnetic head to be less than or equal to 50 nm. In such case, resonance design depending upon the base and the arm becomes important. If stiffness of these members is low, resonance can be caused in low frequency range to rise a servo band for positioning of the magnetic head to make impossible to realize high positioning precision. Therefore, by making stiffness of the arm and base as much as possible, designing has been done for shifting resonance point shifted toward higher frequency range.
Finally, reason why the PCBA is mounted outside of the DE is prevention of penetration of dust or other foreign matter within the DE. In the PCBA, a large amount of corrosive elements contained in solder or flux is present. If such element is housed within the DE, corrosion may be caused in the magnetic head and the storage medium. Therefore, a construction is taken to mount the PCBA on the back surface of the DE after completion of assembling of the DE.
As set forth above, in the conventional magnetic disk drive unit, for realizing high performance and high reliability, a construction is taken to cover the DE with a touch base cover and to arrange the PCBA outside of the DE. Therefore, the weight of the whole unit becomes heavy and impact resistance becomes low. Furthermore, electronic parts mounted on the PCBA is exposed to make handling ability of the unit low. At the present, there is not large capacity hard disk drive unit achieving removing ability and portability. In nature, the magnetic disk drive unit is adapted to be used for stationary type unit (desktop type unit), such as workstation, personal computer and the like. For such purpose, the magnetic disk drive unit of the conventional construction has been sufficient.
However, associating with digitizing of video data in nowadays, demand for storage media which can store the video data and is adapted for removable application, has being getting more and more strong. Currently, in this field, as a useful medium, removable recording medium, such as a magnetic tape, DVD and so forth are typically used. However, in case of the magnetic tape, similarly to the existing VHS video recording type magnetic tape, is far lower in versing-up performance and so forth as compared with DVD. On the other hand, DVD currently available merely achieved storage capacity in the extent of 4.7 GB which is not sufficient to record a movie of two hours in high picture quality.
Therefore, in order to solve the problem set forth above, it becomes necessary to develop a large capacity removable medium employing a magnetic disk drive unit.
A simple type removable magnetic disk drive employing a 2.5 inch size magnetic disk has been available. This merely constructed by packing the conventional magnetic disk drive unit in a portable casing and thus is not satisfactory for porting or carrying a large among of data, such as image data, in view point of performance, capacity, cost or the like.
The followings are problem to be solved in for forming portable type magnetic disk drive unit.
First of all, since the magnetic disk drive unit is generally heavy and is not suited for removable magnetic disk drive unit.
The reason is that major components of the conventional magnetic disk drive unit, such as base, cover and so forth are formed of metal. Therefore, if 3.5 inch disk is employed, the weight of the magnetic disk drive unit becomes 500 g to 1000 g to be low in handling ability as portable precise instrument.
Secondly, since the magnetic disk drive unit has low impact resistance, it is not suitable for removable magnetic disk drive unit.
The reason is that cover member, such as base cover of the conventional magnetic disk drive unit covering DE, is all formed of the metal, fastening of such metal members has to be done by screw. Therefore, an impact acting on the magnetic disk drive unit is directly transmitted to the internal major components, such as carriage, motor and the like. Therefore, the internal major components may be easily damaged.
Thirdly, since the electronic parts mounted on the PCBA is exposed, it is not suitable for the removable magnetic disk drive unit.
The reason is that the conventional magnetic disk drive unit is given importance for reliability and thus mounts the PCBA on outside of the DE for preventing penetration of contaminants into the DE.
Fourthly, the magnetic disk driven unit is high in assembling cost.
The reason is that mounting of the carriage, motor and so forth on the base, fastening between the cover and the base and inmost of joints, screws are used. Such construction using the screws inherently cause substantial loading cost upon assembling to make it difficult in automating. Therefore, reducing the screws as much as possible is desirable in view of assembling cost.
The present invention has been worked out in view of the problems set forth above. Therefore, it is an object of the present invention to reduce weight, improve impact resistance, improve removing ability, easiness of assembling and lower a cost in a magnetic disk drive unit.
According to one aspect of the present invention, a magnetic disk drive unit comprises:
a spindle motor mounting a magnetic disk;
a carriage mounting a magnetic head for recording and reproduction;
a park mechanism for placing the magnetic head retracted from the magnetic disk at stand-by state where recording and reproducing are not performed;
a single rigid frame mounting the spindle motor, the carriage and the park mechanism thereon for forming an assembly;
a casing housing and fixing the assembly, the casing being formed of an elastically deformable material.
With the construction set forth above, the major parts including the spindle motor, the carriage and the park mechanism are mounted on the single rigid frame to form one set of assembly and then housed within the elastically deformable casing and is protected by the common rigid frame to achieve high impact resistance, to facilitate assembling and to reduce number of parts for achieving reduction of weight.
The rigid frame is preferably formed into flat, and the spindle motor, the carriage and the park mechanism are mounted on the common magnetic disk drive unit on the same plane of the rigid frame. Also, the rigid frame may be formed from one piece metal plate with die cutting for further reduction of weight.
The rigid frame may form a part of a stator housing of the spindle motor, and thus the rigid frame may be integral with the spindle motor for further down sizing.
The assembly may be formed with the park mechanism is integrally formed with a part of the rigid frame for placing the magnetic head away from the magnetic disk in stand-by state while recording and reproduction is not performed, and whereby the rigid frame body is integral with the park mechanism for achieving further down sizing.
For avoiding electronic parts from externally exposed, a circuit package for controlling the magnetic disk drive unit is preferably housed within the casing.
One of the rigid frame and the casing is formed with a projection and the other is provided a recess or hole for accommodating the projection by elastic deformation of a part of the casing for securing the rigid frame within the casing. With employing such construction, impact force is not easily transmitted to the major parts. Also, by eliminating screw tightening step to lower production cost.
The casing is a molded resin body including a casing body arranged lower side of the assembly and a cover mating with the casing body for entirely covering the assembly, one of the casing body and the cover is provided with a projection and the other is provided with a recess or hole for establishing enclosing condition by engagement of the projection and recess or hole. With employing such construction, impact force is not easily transmitted to the major parts. Also, by eliminating screw tightening step to lower production cost.
The casing is attached a thin conductive member for preventing accumulation of static electric charge. In the alternative, a conductive film is formed on the surface of the casing for preventing accumulation of static electric charge.
According to another aspect of the present invention, a production process of a magnetic disk drive unit comprises the steps of;
forming a flat rigid frame by one of punching press, etching and wire cutting for one piece of plate member;
mounting a spindle motor mounting a magnetic disk, a carriage mounting a magnetic head for recording and reproduction, and a park mechanism for placing the magnetic head retracted from the magnetic disk at stand-by state where recording and reproducing are not performed for forming one set of assembly;
fixing the rigid frame and an elastically deformable casing for covering the rigid frame therewithin by engaging portions thereof; and
enclosing the assembly with in the casing.